The invention relates to an expansion tank which is intended to be connected to a pipe system which is filled or is to be filled with a liquid, comprising a closed tank with at least one connection opening for a liquid pipe, the tank being provided with a main valve inside the tank, the main valve having a valve seat and a closure member which interacts with the valve seat and being designed to close off the connection opening at a defined difference between the pressure in the interior of the tank and the pressure in the connection opening and/or at a defined liquid level in the tank.
An expansion tank of this type known from, for example, CH-A-397190 and U.S. Pat. No. 3,301,275.
In the known expansion tanks the closure member of the main valve is a float body or connected to a float body. A drawback of the known expansion tanks is that in a situation wherein there is a high-speed liquid flow out of the expansion tank to the pipe system the closure member may dragged along with the liquid flow resulting in a closure of the main valve and a further drop of the pressure in the pipe system. When this happens the difference between the pressure in the interior of the expansion tank and the pressure in the connection opening may become higher than the pressure in the expansion when it was delivered ex works. This is undesirable, in particular when there is still a considerable amount of liquid in the expansion tank at the moment the main valve is closed. In that case it is difficult to bring the pipe system with expansion tank back into the normal operating conditions.
A difference between the pressure in the interior of the expansion tank and the pressure in the connection opening which is higher than the pressure in the expansion tank when it was delivered may also arise if so much gas has been released out of the pipe system into the tank that there is an excessive quantity of gas in the tank.
It is an object of the invention to provide an expansion tank of the above type which does not have the above mentioned drawbacks.